To commence the ebullition of To commence the dissociation of water under ordinary pressure, aqueous vapor under ordinary a temperature of 100° C., or pressures, a temperature of 212° F., must be attained. 2800° C., or 5072° F., must be attained. To complete the ebullition of a To complete the dissociation of given quantity of water, an a given quantity of aqueous amount of heat must be applied, vapor, an amount of heat must sufficient to have raised be applied sufficient to have the water 537° C., or 968° F., raised the vapor 4532° C., or above its boiling-point, had it 8158° F., above its dissociation- not evaporated. point had it not decomposed. In order that a given quantity of In order that a given quantity of vapor of water shall condense, the elements of water may combine, it must give off sufficient heat they must give off sufficient to raise its own weight of water heat to raise their own 537° C., or 968° F. weight of aqueous vapor 4532° C., or 8158° F. I have expressed these generalizations and analogies rather more definitely than they have been hitherto stated, but those who are acquainted with the researches of Deville, Cailletet, Bunsen, etc., will perceive that I am justified in doing so.[2] With the general laws of the dissociation of water thus before us, we may follow out the necessary action of the above-stated pressure and consequent evolution of heat in the lower regions of the solar atmosphere upon the large proportion of aqueous vapor which I have shown that it should contain. It is evident that the first result will be separation of this water into its elements, accompanied with a loss of temperature corresponding to the latent heat of dissociation. We may assume that in the lower regions of the solar atmosphere the free heat evolved by mechanical compression will be more than sufficient to dissociate the whole of the aqueous vapor, and thus the dissociated gases will be left at a higher temperature than was necessary to effect their dissociation. Their condition will thus be analogous to that of superheated steam: they will have to give off some heat before they can _begin_ to combine.[3] There will, however, be somewhere an elevation at which the heat evolved by the joint compression of the elementary and combined gases will be just sufficient to dissociate the latter, and here will be the meeting surface of the combined and the uncombined constituents of water. There will be a sphere containing combined oxygen and hydrogen surrounded by an atmospheric envelope containing large quantities of aqueous vapor, and the temperature at this limiting surface will be equal to that of the oxyhydrogen flame under a corresponding pressure.